The present invention relates to a system for treating waste organic solvent, and more particularly to a system for extracting renewable volatile compounds from waste containing organic solvents such as coating material, thinner, and printing ink, and separately recovering the volatile compounds by means of fractional distillation. The invention also pertains to a thin membrane distillation apparatus, incorporated in the treatment system, for recovering renewable volatile compounds from waste.
Several systems have been proposed for recovering renewable volatile compounds from waste containing organic solvents. FIG. 5 shows an example of the prior art systems, in which a mixture of volatile compounds is distilled from a predetermined amount of waste in a distillation unit 225. As occasion demands, the volatile compound mixture is further cooled and heated in another distillation unit 226, thus being recovered by boiling points via a distillation tower 227. In FIG. 5, numerals 228 and 230 denote condensers, 229 and 231 coolers, and 232 a temporary storage tank.
The system above is, however, batch type and thus has some drawbacks; only a predetermined amount of waste can be treated at one time, and the residue has to be scraped off from the distillation unit for each recovery of the volatile mixture. Namely, the prior art system is time-consuming and inefficient. When the plural volatile compounds are recovered together, troublesome separation is required afterwards. Alternatively, when the volatile compounds are recovered by boiling points, each volatile compound recovered is of rather low quality due to insufficient separation.
It has now been found that the application of thin membrane distillation apparatus to the system so as to improve the efficiency of the recovery. Waste is supplied from above a decompression chamber covered with a heating jacket into the decompression chamber, is sprayed onto the wall within the decompression chamber with rotating thin membrane blades. Volatile mixture thus distilled is recovered from the upper end of the decompression chamber while sludge is discharged from the lower end thereof. The thin membrane distillation apparatus generally employs a knocker disposed on the wall in the vicinity of an outlet for improved discharge of sludge.
Sludge from waste containing organic solvents mainly consists of compounds of high viscosity like various resins and pigments, and thus even a small shock prevents smooth discharge.